A combined cycle gas turbine plant includes both a bypass stack and a heat exchanger. Diverter dampers are used in combined cycle gas turbine plants to divert the gas turbine exhaust gas either up the bypass stack or into the heat exchanger, for example, for heat recovery steam generation. Generally, in a gas turbine generator that has operability in a “combined cycle” mode, sometimes flue gas from the turbine is passed through a heat recovery steam generator (HRSG) and sometimes the flue gas is passed up a flue bypass stack, instead of passing though the HRSG. At the junction between these two flue gas paths, the diverter damper is movable between two positions, the first position wherein the damper is sealed against a seal land in a flow path leading to the HRSG and the second position wherein the damper is sealed against a seal land in a flow path leading to the stack. For reasons of worker safety, environmental protection, system control and energy efficiency, a diverter damper is needed that seals against a seal land to provide substantially complete isolation of the bypass stack from the heat exchanger.
Diverter Dampers may be used in applications other than gas turbine plants, wherever hot flue gases need to be routed from one port to another using a diverter damper blade for isolation of one port.
Generally, the diverter damper includes a door, called a blade. The blade includes a perimeter seal formed by two spaced apart blade seals. Each blade seal extends out from the perimeter of the blade, with one blade seal spaced behind the other. The blade fits into and seals the outlet port to the bypass stack in one position and can be moved into a second position to fit into and seal the outlet port to the heat exchanger. When positioned in either of the outlet ports, the blade seals seat against a seal land around the perimeter of the outlet port. Each seal land presents two sealing surfaces positioned to seal the two spaced apart blade seals. As such, a cavity is formed between the first contacting blade seal and seal land and the second contacting blade seal and seal land. Ambient air is blown into the cavity to create positive pressure and providing a secondary seal that insulates turbine exhaust from passing the diverter damper blade.
The seal land, when no damper blade is sealed against it, is open in the flue gas path and, thereby, exposed to considerable thermal and aerodynamic forces. Also, the force of the blade bearing against the seal land may also sometimes be considerable. Previously known seal lands were, therefore, often prone to deterioration and deformation, due to blade over-pressure or by thermal expansion. Also, the form of previous seal lands tended to convey considerable heat outwardly to the outer casing of the turbine flue gas exhaust conduit causing paint blistering and corrosion on the outer visible housing of the gas turbine and, more importantly, a hazard to personnel passing or working thereby.